Your post is little confusing. Do you want to play audio through bluetooth from your mobile phone or you want to add an AUX connection to your cassette player and then connect it to your mobile using an AUX cable ?
All the picture links you posted don’t work.
When I was in this situation, I had used this FM transmitter thing and used some empty FM frequency to listen my Mp3 songs but this needs MP3 songs to be copied onto a micro SD card.
It was something like this
Now there are modern devices available which get MP3 playback from your mobile through bluetooth and then use builtin FM transmitter so that you can just tune your cassette player to an empty FM frequency and enjoy your music + phone calls wirelessly.
I finally ended up installing Pioneer DEH-X6650BT (CD Player with Bluetooth capability to connect to mobile phones) in all of my cars. Life is smoooooth now.